This invention relates to multichannel surface acoustic wave devices, such as frequency synthesizers and multipliers and, in particular, to means for coupling the multiple transducers thereof to single channel electromagnetic wave input and output transmission lines.
The design of multiplexers, which split a single channel carrying many frequencies into a number of separate channels carrying narrower bands of frequencies, is a problem frequently encountered by design engineers. Similar filter groups are often required for the inverse process of summing a number of channels carrying different bands of frequencies so that all of the frequencies can be put in a single broadband channel with minimum loss of energy.
The inherent properties of surface acoustic wave technology which permit the realization of compact, low cost filter networks are well known. These size and cost advantages also apply to UHF and microwave frequency multiplexer realizations. Furthermore, it is readily possible to utilize their frequency selective features in multiplexer design. In most single-filter design procedures, only the transmission response is considered and little attention is given to the input impedance characteristics. For mulitplexer design, requiring the coupling of N individual filters, the performance of a given channel (filter) is considerably affected by the impedance levels of the remaining channels (filters). In order to obtain desirable low channel insertion losses the surface wave filter input impedances must be carefully considered.
In multiple channel frequency multiplexers and similar multichannel acoustic wave devices much of the loss occurs during the division of the source energy to the individual input transducers. An ideal solution would be a sophisticated matching network; however, the bulk and complexity of the required circuitry would to some extend nullify the inherent compactness and simplicity of the acoustic surface wave filterbank approach.
There currently exists, therefore, the need for simplified means and techniques for coupling mutliple acoustic surface wave transducers to a single channel electromagnetic transmission line. The present invention is directed toward satisfying this need. SUMMARY OF THE INVENTION
The invention comprehends a circuit for coupling the transducers of a multichannel surface acoustic wave device to a single channel electromagnetic wave transmission line. The circuit connects the input (transmitting) transducers into a series or series-parallel arrangement comprising m parallel branches of n series connected transducers. This circuit is connected to the transmission line through an inductor. The inductor has an inductance value that provides minimum insertion loss at the operating center frequency of the acoustic wave device. The transducer connection circuit is selected as the particular series parallel arrangement that provides minimum insertion loss within certain prescribed insertion loss variation constraints.
It is a principal object of the invention to provide a new and improved method for coupling multiple surface acoustic wave device transducers to a single channel electromagnetic wave transmission line.
It is another object of the invention to provide a new and improved electrical circuit for connecting multiple surface acoustic wave device transducers to a single channel electromagnetic wave transmission line.
It is another object of the invention to provide improved coupling means for connecting multiple surface acoustic wave device transducers to a single channel electromagnetic wave transmission line, such coupling means having minimum insertion loss and acceptable insertion loss variation characteristics with a minimum amount of external circuitry.
These, together with other objects, advantages and features of the invention will become more readily apparent from the following detailed description taken in conjunction with the illustrative embodiment in the accompanying drawings.